Composition of matter and process



United States Patent Office "3,363,997 Patented Jan. 16, 1968 3,363,997 CUMPOSITIGN F MATTER AND PROCES James W. Dale, Winchester, Mass, assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Dec. 22, 1953, Ser. No. 781,880 3 Claims. (Cl. 223-356) This invention relates to a high-energy oxidizer compound and to its preparation. More particularly this invention relates to the novel compound nitrosyl chlorotetrafluoride, to processes of preparing same, and to the use thereof as a high-energy oxidizer in rocket propellant combinations.

Considerable research energy has been expended in an effort to find materials which will provide a high specific impulse when employed as propellants in various designs of rockets and missiles. Liquid oxygen is employed as the oxidizer with various fuels in many of the present large rocket systems. However the extreme low temperature required to handle liquid oxygen, below 3-60 F., creates numerous design and handling problems. Also the excessive ready-time of the rocket employing liquid oxygen precludes its effective use as a defensive weapon.

To overcome some of the limitations inherent to the liquid propellant systems, various solid propellant systems have been developed. The solid composite propellant systems have employed solid oxidants such as ammonium nitrate, potassium perchlorate, and ammonium perchlorate with various organic resin fuel-binders. The solid propellant rocket system is characterized by greater hardware simplicity than the liquid propellant system, has a high reliability, can be stored against future need relatively safely, and has a very short ready-time. How ever, the specific impulse of the solid propellant composition is relatively low, e.g. being of the order of from about 210 to 225 sec. for ammonium perchlorate with various fuel-binder compositions.

To provide propellant compositions having higher specific impulse the use of liquid fluorine with various fuels, as for example JP-4, ammonia, diborane, hydrazine, hydrogen, etc., has been proposed. However, since liquid fluorine must be held at temperatures below about 367 F., it is readily apparent that similar problems to those met in the use of liquid oxygen also are inherent with liquid fluorine propellant systems.

The principal object of the instant invention is to provide a novel fluorine oxidizer composition. Another object of the instant invention is to provide a fluorine oxidizer composition which can be employed as the oxidant in rocket propellant compositions without resorting to extreme low temperatures as required for liquid oxygen and liquid fluorine. Still another object of the instant invention is to provide a process for the production of the novel fluorine oxidizer composition. Other objects and advantages of this invention will be apparent to those skilled in the art from the following disclosure.

It has now been found that a new high-energy fluorine oxidizer composition, nitrosyl chlorotetrafluoride, having many of the advantages of liquid fluorine, but which is a solid at least up to temperatures of about 32 F., can be readily prepared from nitrosyl fluoride and chlorine trifiuoride:

Since the chlorine trifiuoride is a powerful oxidizing agent the aforesaid reaction is carried out in equipment fabricated from materials which are inert to the reactant, for example some metals are passivated by the formation of a protective fluoride film which halts further reaction. Examples of particularly suitable materials are mild steel, copper, and nickel. Preferably equimolar quantities of the nitrosyl fluoride and chlorine trifiuoride are reacted at from temperatures of from about 0 C. to about C. and preferably from about 20 C. to about -80 C. Thus gaseous nitrosyl fluoride can be passed over, or through, the liquid chlorine trifiuoride, or mixed with gaseous chlorine trifiuoride and then the mixture can be cooled to effect condensation; or liquid nitrosyl fluoride can be mixed with liquid chlorine trifiuoride by any suitable means and the nitrosyl chlorotetrafiluoride recovered therefrom. Whereas a slight excess of either reactant can be employed and subsequently removed by a brief period of pumping at temperatures below about 20 C. and preferably at about 30 C. or lower, it is preferred that the nitrosyl fluoride be employed in a slight excess over the required equimolar quantity since its higher volatility and lower reactivity in relation to the chlorine trifiuoride facilitate its removal from the nitrosyl chlorotetrafluoride product. Also since nitrosyl fluoride can be prepared with out using free fluorine, it can be considered more expendable than chlorine trifiuoride.

The nitrosyl chlorotetrafluoride can also be prepared by the direct reaction of nitric oxide with chlorine trifluoride at a temperature below about 0 C. and down to about -80 C., eg. by passing the gaseous nitric oxide over the liquid chlorine trifiuoride to produce the intermediate nitrosyl fluoride in situ, which intermediate then reacts with additional chlorine trifiuoride to give the desired product. This series of reactions can be shown by the following equations:

Any chlorine monofluoride, which may not be quantitatively consumed under the selected processing conditions would be readily removed along with the chlorine produced in the reaction when the product is subjected to a brief pumping operation at a temperature preferably between about 20 C. and about 35 C. Since the normal coiling points of chlorine monofiuoride and chlorine are respectively about -l01 C. and -34 C. it will be apparent that the nitrosyl chlorotetrafluoride can be rapidly purified over the above-mentioned temperature range. It Will also be apparent that lower temperatures may be employed in the pumping operations, in which event the pumping operation must be carried out for a longer period of time to effect the substantially complete removal of the chlorine from the product.

Similarly to the above alternative, nitrosyl fluoride can be formed in situ by the reaction of nitrosyl chloride with chlorine trifiuoride followed by further reaction with additional chlorine trifiuoride to give the desired nitrosyl chlorotetrafluoride product, which can be purified by the removal of chlorine and any residual chlorine monofluoride as disclosed above. This series of reactions can be exemplified by the following equations:

NOCl+2F NOClF 2NO+Cl +4F 2NOClF The nitrosyl chlorotetrafluoride is a solid white compound which sublimes at a temperature of about 0 C. under normal atmospheric pressure, and the solid has a density slightly over 1.9 at C. This novel composition is particluarly useful as a high-energy oxidant in a rocket propellant system wherein the fuel can be materials such as ammonia, hydrazine, unsymmetrical dimethyl hydrazine, monomethyl hydrazine, and other nitrogen-rich compounds; diborane; hydrogen; hydrocarbons, and fuel compositions such as JP4; alcohols such as methanol and ethanol; and the like. It has been found, for example, that nitrosyl chlorotetrafluoride together with ammonia provides a hypergolic combination having very high energy. Thus liquid ammonia can be vaporized and sprayed to impinge on the solid nitrosyl chlorotetrafluoride to provide a very brisk flame in a rocket motor which can be controlled by the rate at which the ammonia fuel is fed to the rocket motor. The combustion reaction in the rocket motor can be shown by the equation:

from which it is seen that moles of the solid/liquid propellant yields 23 moles of hot low molecuar weight gases. Thus, it will be seen that this system is capable of providing a very high specific impulse to the rocket system.

Similarly the combustion reaction in the rocket motor employing hydrazine as the fuel therein can be shown by the equation:

wherein 11 moles of the solid/liquid propellant provides 33 moles of hot exhaust gases. From the foregoing, it is seen that the average molecular weight of the rocket exhaust gases closely approaches the low molecular weight theoretically attained with the system liquid fluorine oxidant with liquid hydrogen fuel, which system represents about the maximum specific impulse attainable for the strictly chemical combustion rocket motors. However it will be understood that the average molecular weight of the exhaust gases will be somewhat less than that indicated above, due to dissociation under the rocket motor conditions, just as the average molecular weight of the exhaust gases from the fluorine-hydrogen system is less than the theoretical hydrogen fluoride. Accordingly, it is readily seen that the rocket system employing nitrosyl chlorotetrafluoride as the oxidant therein approaches the high specific impulse of the liquid fluorine/liquid hydrogen system without the very serious disadvantages of the extreme low temperature requirements of the said liquid system.

The following examples are illustrative of the instant invention.

EXAMPLE 1 Nitric oxide was generated by the dropwise addition of sulfuric acid to a solution of sodium nitrite. The evolved gas was passed in sequence through a caustic bubbler containing 4-normal aqueous potassium hydroxide solution, a liquid caustic scrubber containing 4-normal aqueous potassium hydroxide solution, a bed of solid potassium hydroxide and then through a tube containing phosphorus pentoxide, whereby the higher oxides of nitrogen, carbon dioxide and moisture were removed from the nitric oxide.

Substantially equimolecular quantities of the gaseous nitric oxide and gaseous chlorine trifluoride were introduced continuously in close proximity through copper tubing into a water-cooled, jacketed, tubular copper reactor (1.5 O.D.), to effect reaction of the mixed gases. The reaction product was collected in a trap, cooled in Dry Ice-trichloroethylene mixture, protected by a second trap cooled in liquid air to preclude any moisture from sucking back into the system. The product was subjected to a reduced pressure of about 20 mm. of mercury, at about 30 C. for about 15 minutes to remove any excess reactants. Then the white solid reaction product was recovered and noted to sublime at about 0 C. The prodnot was found to spontaneously ignite wood and paper when contacted therewith in air. A 3-gram sample of the product was placed in a copper cup suspended in a nickel bomb containing ml. of 4-no1'mal aqueous potassium hydroxide solution, the bomb sealed, contents mixed and heated to hydrolize the product, then cooled and the solution analyzed for fluorine, chlorine, and nitrogen.

Calculated for NOClF.,: F, 53.71; Cl, 25.08; N, 9.89. Found: F, 54.9; C1, 24.5; N, 9.44.

EXAMPLE 2 A sample of liquid chlorine trifluoride was cooled and held at -30 C. in a vessel immersed in a mixture of Dry lce-trichlorethylene. Anhydrous nitric oxide was then passed over the surface of the chlorine trifluoride and a white solid was observed to form therein. The flow of nitric oxide was continued until the chlorine trifluoride was completely converted from the liquid to the solid white nitrosyl chlorotetrafluoride product.

EXAMPLE 3 Nitrosyl fluoride was generated by passing anhydrous nitric oxide and fluorine through the tubular copper reactor described in Example 1.

A sample of liquid chlorine trifluoride was cooled and held at -30 C. in a vessel immersed in a Dry lce-tri chloroethylene mixture, and the nitrosyl fluoride was passed over the chlorine trifluoride, which was observed to be converted to the white solid nitrosyl chlorotetrafluoride product in a substantially instantaneous reaction.

EXAMPLE 4 In similar fashion to Example 2, liquid chlorine trifluoride was held at about 30 C. and gaseous nitrosyl chloride was passed thereover. The nitrosyl chloride was converted to nitrosyl fluoride which reacts with the chlo rine trifluoride to give the solid white nitrosyl chlorotetrafluoride product.

EXAMPLE 5 To illustrate the utility of nitrosyl chlorotetrafluoride as a solid high-energy oxidant it was observed that when a stream of ammonia was directed against the exposed surface of the nitrosyl chlorotetrafiuoride it was ignited to produce a vigorous flame. By terminating the flow of ammonia the combustion reaction ceased, but the vigorous flame was immediately reformed when the flow of ammonia was again started. It was observed that the solid oxidant remained intact between each application of ammonia. Thus, this propellant system, in contradistinction to a conventional solid propellant system, is subject to control to provide flame-out at the proper time when the missile is in flight whereby the desired glide path to the target will be followed.

The high-energy oxidizer is also hypergolic with many other fuel components. Thus, in the hydrocarbon fuel series, even the higher boiling portion of the volatile petroleum fraction, i.e. ligroin, readily bursts into flame when brought into contact with nitrosyl chlorotetrafluoride.

In a similar fashion various other fuels and fuel mixtures can be employed with the solid oxidant to provide the energy for propelling rockets and missiles.

The nitrosyl chlorotetrafluoride can also be employed as an intermediate in the preparation of various other fluorine-containing compounds in similar fashion to chlorine trifluoride.

I claim:

1. The process of preparing nitrosyl chlorotetrafluoride comprising reacting nitrosyl chloride and chlorine trifluoride in a mole ratio of about 3 to 4 and recovering the solid nitrosyl chlorotctrafiuoride by removal of any residual reactant in the system under reduced pressure while 5 holding the system at a temperature of from about 20 to about 35 C.

2. The process of preparing nitrosyl chlorotetrafluoride comprising reacting nitrosyl chloride and fluorine in a mole ratio of about 1 to 2 and recovering the solid nitrosyl chlorotetrafluoride by removal of any residual reactant in the system under reduced pressure While holding the system at a temperature of from about 20 to about -3S C.

3. The process of preparing nitrosyl chlorotetrafluoride comprising reacting nitric oxide, chlorine, and fluorine in a mole ratio of about 2:1:4 and recovering the solid nitrosyl chlorotetrafluoride by removal of any residual reactant in the system under reduced pressure while holding the system at a temperature of from about -20 to about 35 C.

References Cited UNITED STATES PATENTS 2,721,792 10/1955 Hannum 52O.5 2,768,888 10/1956 Ryker 520.5

OTHER REFERENCES 10 Woolf: J. Chem. Soc, London, pp. 10531056 Simons: Fluorine Chemistry, vol. I, pp. 89, 90, 189200 (1950).

Mellor: Comprehensive Treatise on Inorganic and 5 Theoretical Chemistry, vol. VIII, p. 612 (1947).

MILTON WEISSMAN, Primary Examiner.

'MAURINE BRINDISI, LEON D. ROSDOL, ROGER L. CAMPBELL, Examiners.

C. D. QUARFORTH, Assistant Examiner. 

1. THE PROCESS OF PREPARING NITROSLYL CHLOROTETRAFLUORIDE COMPRISING REACTING NITROSYL CHLORIDE AND CHLORINE TRIFLUORIDE IN A MOLE RATIO OF ABOUT 3 TO 4 AND RECOVERING THE SOLID NITROSYL CHLOROTETRAFLUORIDE BY REMOVAL OF ANY RESIDUAL REACTANT IN THE SYSTEM UNDER REDUCED PRESSURE WHILE HOLDING THE SYSTEM AT A TEMPERATURE OF FROM ABOUT -20* TO ABOUT -35*C. 